AMD Fam15tn: Add support for AGESA runtime allocation in CBMEM

The IOMMU AGESA needs a reserved scratch space and it wants
to allocate the stuff for runtime. So provide a simple
allocator for 4 KB CBMEM page.

Change-Id: I53bdfcd2cd69f84fbfbc6edea53a051f516c05cc
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/3315
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/include/cbmem.h

@@ -71,6 +71,7 @@
 #define CBMEM_ID_VBOOT_HANDOFF	0x780074f0
 #define CBMEM_ID_CAR_GLOBALS	0xcac4e6a3
 #define CBMEM_ID_NONE		0x00000000
+#define CBMEM_ID_AGESA_RUNTIME	0x41474553
 
 #ifndef __ASSEMBLER__
 #include <stdint.h>